Soldering heavy wire

A proper soldering iron although if like me you use welding cable the heat disapation is so quick as to make the blow torch a necessity.
The proper soldering irons I use are old fashioned 19thc tin smiths irons and once you get one of the big ones hot with a blow torch they seem to solder anything-starter motor and alternator cable no problem..
I keep a neat little one on board for general purpose wiring work etc-just heat it on the stove for five minutes.
 
Unless you've access to something like the irons ffiill describes I'd go for the crimp option too. Just take them to a proper garage (i.e not BMW/Audi main dealers, etc) or truck/agricultural machinery repair shop - they should have all the gear to do them.
 
Whatever method you use, finish the job off with adhesive lined heat shrink. That way it won't matter if a small amount of insulation has melted.

J
 
My blowtorch has a soldering attachment just for this sort of thing. It gets very hot so is very quick to heat a local area on thick wire so minimises melting of close insulation. As has been said have some heat shrink tube slid down the wire and then slide it up to finish off. Holding the blowtorch bit close will shrink it.
 
Put the crimp on the wire and then hold the crimp in either a blow torch or gas ring and be ready to feed in the solder. Works a treat. That said there are cheap enoug crimpers on the internet and they do make an excellent job. Which ever way you go finishing with heat shrink makes a nice tidy job.

Yoda
 
Whilst on this subject I use welding cable for battery connections-as I said very quick heat disappation due to the multiple fine wire strands but really very flexible when working/using in the confines of a small space.
 
A big soldering iron is easier/safer.
For this size around 80w will do, but if you buying one go bigger so you can do larger diameter wire. Large irons like this are available quite cheaply they don't need to be good quality temperature controled units.

I feel it is essential to at least do a crude crimp on these wires. Without this if the joint overheats and the solder melts the wire can pull out of the terminal. Wires of this diameter can produce a serious short.
The crimp just provides mechanical support for the wire and the solder provides a good electrical connection.

Even a vice will make a mechanically strong crimp. Pull the wire to test it is securely held then solder. The soldering is also easier and more reliable when the wire is firmly held.

Add some glue lined heat shrink to finish.

An alternative is GOOD crimp to provide both the mechanical and electrical connection. Unfortunatly the crimps I see amateurs do on large wires are often very poor. To crimp correctly you need good tools (which are expensive in large sizes) and good quality matched terminals and wire sizes which are difficult to find in out of the way places.
Soldering fixes these problems.
 
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The technique is simple really though needs practice to get an aesthetic finish. It is good for any size including and above 16mm.
The cable shoe (the fitting) should be the type without a small hole in the tube side. Those are for crimping not soldering and are to allow you to see that the conductor is fully inserted into the socket.
Hold the shoe in a vice or a pair of grips on a metal surface leaving as much as possible exposed without the fear of it moving during the process. The shoe should be held so the socket stands vertically.
Apply a little flux to the inside.
Cut the cable insulation back so it clears the shoe by about 1/2 inch when fully inserted into the socket. A little melting of the insulation edge is inevitable as the conductor has to be sufficiently warm as to melt the solder.
Apply a little flux to the cable.
Insert the cable fully into the shoe socket. It should enter straight into the socket and not at an angle as this is how it will stay once soldered. Some support may be needed to achieve this.
Play the flame from a gas torch to the shoe at the bottom end of the socket away from the cable entry.
After a short while offer the solder wire to the conductor to see if the conductor has now become warm enough to melt the solder. Don't offer the solder to the shoe as this will get warm before the conductor and fill the socket with solder and give a poor result in that solder will not have flowed throughout the conductor strands.
Once the solder starts to melt on the conductor continue to feed it into the socket until the socket is full during which and at the same time having removed the flame from the shoe so as not to 'over' heat the conductor as this will make the solder wick too far up the cable. Ensure that solder comes fully to the top of the socket as it will have a layer of flux floating on top of the molten solder which will deceive you and when cleaned you will have a socket only half full.
Use wire wool or scotch pad to 'flick' off any overspill of solder on the outside of the shoe.
At this point do not move either cable or shoe at all for a minute.
Allow two minutes for it to solidify. Clean off all traces of flux and any excess solder on the outside of the shoe wall. Cover shoe socket and lower inch or two of cable with quality heat shrink or tape of your choice.
Job done.
When practiced takes no more then 3 minutes and is the best joint you'll get.
Simples.
 
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